Chlorine Residual Monitoring and Pocket Colorimeters

During sanitary surveys, inspectors evaluate where chlorine residual sampling is being performed and will request to do side-by-side chlorine residual measurements with the operator. Chlorine residual monitoring is required both for entry point chlorine residual monitoring and also in the distribution system during bacteriological sampling. Public water systems that only use sodium or calcium hypochlorite or chlorine gas to form free chlorine for disinfectant residual should be monitoring and reporting free chlorine residual at all times. Conversely, any systems adding ammonia to form chloramines must monitor and report disinfectant residual as total chlorine residual. In this article, we will discuss handheld colorimeters and questions we’ve received from operators during sanitary surveys on properly measuring both high range and low range chlorine residuals. Improperly using an EPA accepted test method, using expired or incorrect DPD reagent or not verifying or operating disinfectant monitoring analytical equipment in accordance with manufacturer requirements can result in a violation of Regulation 11, Section 11.46. This was one of the Top 10 most cited violations cited during sanitary surveys in 2022.

The main issue inspectors often see in the field is measuring low range vs. high range free chlorine residual. For HACH pocket colorimeters (PCII) in the low range (LR) setting, a readout of 2.2 will flash repeatedly if the sample concentration is above 2.2 mg/L free chlorine. Recording the 2.2 mg/L as the chlorine residual is not correct and will result in a violation during a sanitary survey. The operator should be familiar with how to change their chlorine analyzer setting from low to high range. For a HACH DR300 or a HACH PCII, you must select the High Range (HR) menu option (please see your manual). For HACH units in High Range, the sample cell also changes to the plastic vial with a 5-mL sample and two 10‑mL DPD Free Chlorine Reagent Powder Pillows or two 10‑mL DPD Total Chlorine Reagent Powder Pillows must be used for each test. Please see your manual for your specific chlorine residual kit, and note that some manuals have to be downloaded online now.

Other issues that can result in field based violations for chlorine residual monitoring is using expired DPD reagent and glassware that is caked with DPD (see photo below). 

Operators must be familiar with their colorimeter and should have written maintenance procedures and a maintenance log implemented for the analyzer, including routine verifications required by the manufacturer (HACH does not specify a frequency for pocket colorimeters but CDPHE does quarterly checks with GELEX standards on our pocket colorimeters). Please note that for online chlorine analyzers used for compliance with Regulation 11, online analyzers must be verified at least once a week by taking a parallel grab sample and analyzing it by another verified method (bench top) or by comparison with other parallel analyzers (see Policy 4 Guidance). All verification checks and results should be written down in a logbook.

Please avoid these field-based violations related to chlorine residual monitoring and ensure proper disinfection by being familiar with your analyzer and following proper sampling protocol. For any questions or concerns, please email our Field Services team at cdphe_wqcd_fss_questions@state.co.us.  

➽ Connor Clarke, CWP, Field Services Section

➽ Heather Young, PE, CWP Field Services Section

Program Manager's Message: Draft PFAS Rule Considerations

We finally reached the stage where EPA is nearing the completion of the process that leads to a new drinking water rule being added to the Safe Drinking Water Act to address per- and polyfluorinated alkyl substances (PFAS). This has been a long journey, and there is still a ways to go before a rule is in place and implemented. Several years ago two PFAS compounds, PFOA and PFOS, were part of the third Unregulated Contaminant Monitoring Rule (UCMR3). We started working to address PFAS in drinking water in 2016 after we became aware of their presence in drinking water at several communities in El Paso County. Our efforts continued through the 2020 sampling project and today in implementing the updated PFAS health advisory EPA issued in June 2022.

EPA made the decision to regulate PFAS under the Safe Drinking Water Act in late 2021 and in March 2023 published a draft rule for public comment. The draft rule for PFAS establishes Maximum Contaminant Levels (MCLs) for PFOA and PFOS at 4 parts per trillion (ppt) and a novel (at least within the Safe Drinking Water Act) Hazard Index approach to address four more PFAS compounds - PFNA, PFHxS, GenX and PFBS. Of these, PHHxS which is often associated with firefighting foam has been detected most often in Colorado. During its fifth Unregulated Contaminant Monitoring Rule (UCMR5) testing EPA is again sampling for multiple PFAS compounds, so more of these may be addressed in future rule revisions. 

EPA indicated that after the public comment period on the draft rule, it anticipates finalizing the PFAS rule in early 2024. States typically have two years to adopt a final rule, and then the compliance date follows a year of initial monitoring. So the compliance date for this rule would be sometime in 2027 if the normal schedule is followed.

EPA structured this draft rule to model other chronic organic contaminants with quarterly monitoring and compliance based on a running annual average of those results. Reduced monitoring options are available. Violations of the MCL or Hazard Index would result in Tier 2 public notice. We support this approach as compared to a possible approach treating violations as an acute health risk warranting Tier 1 public notice.

There is a significant need for EPA guidance on this rule that addresses treatment design and conduction pilot studies, residual waste handling and disposal, reduced monitoring and the trigger level, public notice and communications and much more. This is very important to foster state implementation and water system compliance. 

We believe that there are many feasibility concerns associated with addressing PFAS contamination in drinking water generally, and these become even more challenging with MCL values set at the practical quantitation limit that many laboratories can reliably achieve. Although the laboratory Colorado has been using can get lower values than the MCLs, this one laboratory will not be able to serve all the water systems that need to test. Lab capacity could become a significant problem, and the turnaround time to obtain results could also become very slow.

This rule will also require significant new resources to implement. Colorado has been able to implement several new rules the last decade involving disinfection, water haulers, storage tanks, backflow prevention and cross connection control, and the revised total coliform rule without adding program resources for implementation. However, with this PFAS rule coming essentially at the same time as the Lead and Copper Rule Revisions (LCRR) and the Consumer Confidence Rule (CCR) revisions, the division must obtain additional resources to support maintaining primacy into the future.  

In addition to feasibility concerns with laboratory capacity and program resources, financial resources for water systems to secure compliance will also be needed. The State Revolving Fund and Bipartisan Infrastructure Law have provided a boost, but this will not be enough funding for all the needed projects. These funding sources help with initial design and construction activities, but do not help with the long-term operating and maintenance costs. For PFAS, residual handling and disposal costs are likely to be high, and these costs will need to be borne by water utilities and ultimately rate payers. Small systems will face special challenges with the costs and need for higher operator certification levels if treatment needs to be installed. 

As always, we will be engaging stakeholders in developing the PFAS rule for Colorado. Fortunately, we have many staff that are experienced with PFAS that understand the issues and challenges, and have been helping water systems address contamination. This will enable us to identify assistance, policy and training needs. We will strive to help water systems meet the requirements of the PFAS as best we can considering our funding and resource levels. Our goal will be to get as many systems as possible into compliance before the required deadline. I advise you to learn about the new draft PFAS rule and take steps to prepare your water system for it. If you have not yet collected PFAS samples from your system, I advise you to contact us and we will test your water for free. Getting in front of this now while funding is available is the best approach to keeping tap water safe for your customers. 

Thank you,

➽ Ron Falco, P.E. Safe Drinking Water Program Manager

Lessons Learned - Weld county legionella cluster

What Occurred?

In November and December of 2022, the Weld County Public Health Department consulted with CDPHE about an unusual number of cases of Legionnaires Disease occurring in a relatively small area. There were five reported cases of the illness and case interviews were completed for four of the five affected people. Excerpt from the internal communications at the time:

"We have recently seen a notable increase in reported legionella infections in Weld County – five cases in the last 12 days. Of the three most recent cases, two live within two miles of each other and one lives within seven miles of the other two. We have not yet found any evidence of linked exposures."

In a situation where a cluster of illnesses is identified and there is a potential for the root cause of the illness to be drinking water, public health partners work with the Safe Drinking Water Program here at CDPHE to assess the likelihood/possibility that the drinking water is the root cause of the cluster (or waterborne disease outbreak).

What was the Response?

Based on initial interviews with the ill folks, the county determined that there appeared to be a lack of common exposures that are usually seen. Typically in a legionella outbreak, you may find that all infected people used the same recreation center hot tub or shop at the same grocery store that has vegetable misters running. 

The county and state epidemiologist group then reached out to the Safe Drinking Water Program staff to check the known addresses of the ill people to see if they were served by the same water system and if it was possible that a contamination event had occurred at that specific water system. We specifically were trying to determine whether there had been any service disruptions, major construction projects, water main breaks, or other events related to the water utilities that service these individuals' residential areas. 

The Safe Drinking Water Program then interfaced with water system operational staff to confirm whether there had been any water quality issues in these areas. Also, it was determined that these homes- while being in proximity to each other, were served by four different water providers. All providers demonstrated robust chlorine residuals and were able to show a lack of bacteriological contamination in their drinking water.

While the specific cause of this outbreak was never determined, public drinking water was eliminated as a source.

What can a water operator do to prepare for such an event?

If a cluster of illnesses occurs in your service area, you may be called upon to produce records of treatment and distribution system water quality in order to eliminate any potential that your drinking water caused the illnesses. 

Maintaining treatment plant records is standard procedure for most public water systems.  However, having a comprehensive distribution system microbial sampling that goes beyond the minimums of the total coliform rule is more rare. Consider developing water quality sampling starting with distribution system basic water quality parameters like chlorine residual, pH, turbidity and heterotrophic plate count. This will help provide assurance that your distribution system water quality is not the cause of a legionella outbreak. Also, water sampling for legionella can be done on a quarterly or semi-annual basis to provide further assurances to the public that the drinking water quality you provide to your customers is safe and relatively pathogen free. 

➽ Tyson Ingles, Lead Drinking Water Engineer